(c) For $\theta = 45{^\circ}$
$H_{\max} = \frac{u^{2}\sin^{2}{45{^\circ}}}{2g} = \frac{u^{2}}{4g}\ \ \ \ \ \ \ \left\lbrack \because\sin{45{^\circ}} = \frac{1}{\sqrt{2}} \right\rbrack$
$R = \frac{u^{2}\sin{90{^\circ}}}{g} = \frac{u^{2}}{g};\ \therefore\frac{R}{H} = \frac{u^{2}}{g} \times \frac{4g}{u^{2}} = 4 \Rightarrow R = 4H$